1. Field of the Invention
This invention relates to a torque transmission apparatus including a fluid-type torque converter including a pump impeller connected to an input shaft and a turbine runner and a stator which are connected to an output shaft, and a direct coupling clutch for mechanically connecting the input shaft and the output shaft to each other.
2. Description of the Prior Art
A torque transmission apparatus of the type, in general, includes, a first circular coupling element engaging the other clutch element of a direct coupling clutch, in a manner to permit a relative movement to the other clutch element in the axial direction thereof, one clutch element of the direct coupling clutch being connected to an input shaft or an output shaft; second and third circular coupling elements coupled to each other at a spacing from each other in a manner to effect a relative rotation to the first circular coupling element through a given angle; and compression coil springs by the first circular coupling element and engaging the second and third circular coupling elements, so as to absorb shock due to the relative rotation of the first circular coupling element to the second and third circular coupling elements; the compression coil springs being adapted to cyclically compress and expand upon receiving a changing torque of an engine which is introduced by way of the input shaft, thereby relieving a changing torque to transmit same to the output shaft.
In this connection, because of a difference in surface hardness between the compression coil springs and the spring retaining portions of the first circular coupling element and the engaging portions of the second and third circular coupling elements, either the compression coil springs or the sliding portions of the first, second and third circular coupling elements, which are lower in surface hardness, suffer severe wear, thus impairing the durability of the direct coupling clutch.